The invention relates to a method for attenuating sound in a duct, the sound to be attenuated being detected in the method by means of a detector and the attenuation being performed by means of two successive actuator elements.
The invention also relates to an equipment for attenuating sound in a duct, the equipment comprising a detector for detecting the sound to be attenuated and two successive actuator elements for producing a sound attenuating counter-sound.
One of the methods presented for attenuating sound in ducts is a method known as the Swinbanks method, in which an attenuation sound is produced by means of two successive elements. Both elements produce a volume velocity of an equal amplitude, the volume velocities being, however, of opposite phases. In addition, to the element that is first in the direction of propagation of the sound to be attenuated is caused a delay proportional to the distance between the elements. A unidirectional, radiating element is thereby obtained, i.e. no acoustic feedback is caused to the detector measuring the sound to be attenuated. Instead, a signal is generated that only attenuates forward the sound of the sound source to be attenuated. To digitally implement inter-channel delay in different elements occupies, however, a great amount of signal processing resources, which means that the equipment to be used must have an extensive capacity and/or the processing time becomes inconveniently long.